The Google search engine found at http://www.google.com offers many features, including language and document translation; web, image, newsgroups, catalog, and news searches; and more. These features offer obvious benefits to even the most uninitiated web surfer, but these same features offer far more nefarious possibilities to the most malicious Internet users, including hackers, computer criminals, identity thieves, and even terrorists. This article outlines the more harmful applications of the Google search engine, techniques that have collectively been termed "Google Hacking." In 1992, there were about 15,000 web sites, in 2006 the number has exceeded 100 million. What if a simple query to a search engine like Google such as "Hackable Websites w/ Credit Card Information" produced a list of websites that contained customer credit card data of thousands of customers per company? If the attacker is aware of a web application that stores a clear text password file in a directory and wants to gather these targets, then he could search on "intitle:"Index of" .mysql_history" and the search engine will provide him with a list of target systems that may divulge these database usernames and passwords (out of a possible 100 million web sites available). Or perhaps the attacker has a new method to attack a Lotus Notes web server and simply wants to see how many targets are on the internet, he could search on "inurl:domcfg.nsf". Apply the same logic to a worm looking for its new victim.

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When web content is indexed by Google their Crawler referred to as "Googlebot" refers to the robots.txt file in the web root directory.

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If the robots.txt file is not revised during changes to web content, then it is possible for web content not intended to be included in Google's Search Results to be indexed by Google.

Brief Summary

This section describes how to retrieve and remove the web content stored by the Google Cache of the application being tested.

This procedure is applicable to other Search Engines such as Live, Yahoo!, etc.

Description of the Issue

When web content is indexed by Google their Crawler referred to as "Googlebot" refers to the robots.txt file in the web root directory.

If the robots.txt file is not revised during changes to web content, then it is possible for web content not intended to be included in Google's Search Results to be indexed by Google.

Therefore, this web content must be removed from the Google Cache.

Black Box testing and example

Description and goal

The scope of this activity is to find information about a single web site published on the internet or to find a specific kind of application such as Webmin or VNC.
There are tools available that can assist with this technique, for example googlegath, but it is also possibile to perform this operation manually using Google's web site search facilities. This operation does not require specialist technical skills and is a good way to collect information about a web target.

Useful Google Advanced Search techniques

Use the plus sign (+) to force a search for an overly common word. Use the minus sign (-) to exclude a term from a search. No spaces follow these signs.

To search for a phrase, supply the phrase surrounded by double quotes (" ").

A period (.) serves as a single-character wildcard.

An asterisk (*) represents any word —- not the completion of a word, as is traditionally used.

Google advanced operators help refine searches. Advanced operators use the following syntax: operator:search_term . Notice that there is no space between the operator, the colon, and the search term. A list of operators and search terms follows:

The site operator instructs Google to restrict a search to a specific web site or domain. The web site to search must be supplied after the colon.

The filetype operator instructs Google to search only within the text of a particular type of file. The file type to search must be supplied after the colon. Don't include a period before the file extension.

The link operator instructs Google to search within hyperlinks for a search term.

The cache operator displays the version of a web page as it appeared when Google crawled the site. The URL of the site must be supplied after the colon.

The intitle, allintitle operator instructs Google to search for a term within the title of a document.

The inurl, allinurl operator instructs Google to search only within the URL (web address) of a document. The search term must follow the colon.

The info operator instructs Google to search only within the summary information of a site

The phonebook operator instructs Google to search business or residential phone listing.

The stocks operator instructs Google to search for stock market information about a company.

The following are a set googling examples (for a complete list look at [1]):

Test:

site:www.xxxxx.ca AND intitle:"index.of" "backup"

Result:

The operator site: restricts a search in a specific domain, while the intitle: operator makes it possibile to find the pages that contain "index of backup" as a link title of the Google output.
The AND boolean operator is used to combine more conditions in the same query.

The query produces an output with every Webmin authentication interface collected by Google during the spidering process.

Test:

site:www.xxxx.org AND filetype:wsdl wsdl

Result:

The filetype operator is used to find specific kind of files on the web-site.

How can you prevent Google hacking?

Make sure you are comfortable with sharing everything in your public Web folder with the whole world, because Google will share it, whether you like it or not. Also, in order to prevent attackers from easily figuring out what server software you are running, change the default error messages and other identifiers. Often, when a "404 Not Found" error is detected, servers will return a page like that says something like:

Not Found
The requested URL /cgi-bin/xxxxxx was not found on this server.
Apache/1.3.27 Server at your web site Port 80

The only information that the legimitate user really needs is a message that says "Page Not found." Restricting the other information will prevent your page from turning up in an attacker's search for a specific flavor of server.
Google periodically purges it's cache, but until then your sensitive files are still being offered to the public. If you realize that the search engine has cached files that you want to be unavailable to be viewed you can go to http://www.google.com/remove.html and follow the instructions on how to remove your page, or parts of your page, from their database.

Using a search engine to discover virtual hosts

Live.com, another well-known search engine (see link at the bottom of the page), provides the "ip" operator, which returns all the pages that are known to belong to a certain IP address. This is a very useful technique to find out which virtual hosts are configured on the tested server. For instance, the following query will return all indexed pages belonging to the domain owasp.org: